i will have to check. this ignition is very strange - it's a bosch, all electronic, but it still has an external condenser... if i could figure out how it worked, it might work. the 'cdi' for it is still available, but it's 40 year old stock...and not too expensive ($90 ish) - it's what i have on there now. i haven't replaced the coil (it's a bosch 2 wire like on many mopeds)...it's available new inexpensively.. i have replaced wire, and plug end, and added an additional ground. i'd like to get flywheel remagnetized - but not sure who does it in usa..

2 sets of pics, 1st set of pics is br9eix run for about 1.5 hours. 2nd set is br8eg run for 5 minutes just putting around to get some color on it. both are identical jetting, ambient temperature/elevation. on the first set of pics, the float level was bit low. also, timing was more retarded (just 1 degree less advance).

i'm thinking the first plug (which still ran fine) was a bit too cold, and a little rich. i'm assuming the carbon deposits all over is just due to plug too cold. there are no seal leaks.

2nd set of pics still a little rch somewhere, maybe hot enough of a plug now to burn deposits off.

1st plug.

2nd plug

...but I thought I would just comment since I work for the company (NGK) that makes the plugs you are using.

Those deposits are not a heat range problem. Looks like too much oil. Are you sure you didn't have a bad crank seal on the wet (tranny oil) side?

The heat rating only affects the temperature of the center electrode ceramic - not the side electrode. There are heavy oil carbon deposits all over the firing end of that plug. It's not a spark plug or heat range problem.

I see that you mentioned that the spark seems fine. It's hard to tell without actually measuring the voltage required to jump the gap. If by chance you had a really weak spark then it could affect the combustion - but it's kind of rare to have enough spark to light the mixture but not do it well enough that it would create those heavy deposits (Hopefully that sentence makes sense).

I would guess that you will still have those heavy deposits even if your ignition system was in tip-top shape. The spark itself will not clean off that kind of crud. The spark intensity and the heat range are completely separate things and do not affect each other at all. (Auto manufacturers have tried and found that there is no measurable correlation.) A "hotter" spark does not heat the end of the spark plug. In conventional ignition systems, a "hotter" spark only occurs when you increase the voltage required to jump the gap. For example, widening the gap will bring the voltage level up because it takes more voltage to jump the gap. But the temperature of the center electrode ceramic will not change.

That being said, there are ways to help prevent fouling by running the spark over the edge of the ceramic, as on a semi-surface discharge spark plug. But that will not really help your problem.

If you ever see this post I would like to find out what you did to fix it.

The first plug looks like transmission oil being sucked into the motor, through drive side crank seal or possibly damaged crankcase gasket.

All CDI based ignitions suffer from reduced spark intensity over the years. This is due to the capacitor degrading, which results in less power going to the HT coil when the system is triggered.

On almost all AC systems with an external CDI unit, its possible to replace them with a cheap pit-bike part costing less than $20.

Finally its very difficult to get accurate plug colour readings when modern fuels are being used in 2T motors, but using a specific race oil such as Castrol XR77 developed to help give accurate readings, will make plug readings much less a matter of pinning the tail on the donkey as it were.